1. Field of the Invention
This invention relates to precision motion stages and more specifically to a stage suitable for use in a lithography machine and especially adapted for supporting a reticle.
2. Description of the Prior Art
In semiconductor manufacture, a medium such as light or non-visible radiation (e.g., DUV or a charged particle beam) is projected through a xe2x80x9creticlexe2x80x9d (or mask) to pattern a resist on a wafer to allow selective processing. Positioning a reticle during these lithography processes has been accomplished by a stage that supports the reticle. An illumination system illuminates a reticle supported on a reticle stage and a lens system projects the reticle pattern on a target. The reticle has a specified pattern, such as a circuit, formed on the surface that is to be projected by a projection exposure system, onto the surface of a wafer, while the wafer is positioned on a xe2x80x9cwafer stagexe2x80x9d separate from the reticle stage. Accurately positioning the reticle is important, so that the corresponding wafer will be made as intended to produce, for example, an array of many electric devices.
Conventional reticle stages provide relatively precise motion in the X-axis and Y-axis directions, and sometimes slight motion in the vertical (Z-axis) direction. A reticle stage is generally used when the reticle is scanned to facilitate compensation of aberration. Conventional stages attempt, with varying degrees of success, to provide as smooth and precise scanning motion as possible, and accurate reticle to wafer alignment. xe2x80x9cYawxe2x80x9d, or rotation in the X-Y plane, is another problem in conventional reticle stages.
Most conventional reticle stages have been two-dimensional (sometimes referred to as xe2x80x9cXYxe2x80x9d) (e.g., U.S. Pat. No. 6,188,195 issued Feb. 13, 2001, to Lee, entitled xe2x80x9cExposure Method, and Method of Making Exposure Apparatus Having Dynamically Isolated Support Structure). Another development in a two-dimensional stage was one in which force generating elements of the stage assembly are supported by a xe2x80x9creaction framexe2x80x9d independent from the electron beam or optical column and from the weight of the reticle stage plate. U.S. Pat. No. 6,130,490 that issued Oct. 10, 2000, entitled xe2x80x9cX-Y Stage with Movable Magnet Platexe2x80x9d is exemplary of such an arrangement.
Also, reticle stage technology has developed based on the recognition that the guide structure that was located in early reticle stage designs directly under the reticle stage interferes with directing light or an e-beam and may cause position degradation and a source of transmitted vibration through the reticle and through the stage to the underlying projection lens. Hence, efforts began to remove the guides and so-called xe2x80x9cguidelessxe2x80x9d reticle stages have been developed.
While reticle stage technology mainly has been in the area of XY stages, recently introducing a third degree of freedom to reticle stage movement has been proposed. U.S. Pat. No. 6,147,421, to Takita, Novak and Hazelton, entitled xe2x80x9cPlatform Positionable in at least three degrees of freedom by interaction with coilsxe2x80x9d mentions wafer positioning and reticle positioning. Takita et al. provide a platform positionable in at least three degrees of freedom by using a system of multiple magnets and multiple coils. Magnets are attached to the platforms and interact with coils to provide motion. Takita et al. make use of inner and outer platforms coupled by magnet bearings so that the inner platform is capable of relative motion with respect to the coils.
Reticle stage systems that have been proposed of the three-degree-of-freedom type do not necessarily permit easiest access to other parts of a photolithography system, nor do they necessarily provide maximal freedom in the third dimension.
The invention provides a three-degree-of-freedom precision stage which is suited for use as a reticle stage in photolithography manufacturing equipment. Additionally, this invention can be used for a wafer stage instead of a reticle stage as far as permitted.
For realizing such advantages, the invention in a preferred embodiment provides an apparatus comprising: a stage; a reaction force countermass assembly; and an anti-gravity device between the reticle stage and the reaction force countermass assembly. The anti-gravity device is configured to offset the weight of the stage to the reaction force countermass assembly.
In a second preferred embodiment, the invention provides a method of offsetting weight of a stage to a reaction force countermass assembly, comprising the step of: for a stage and a reaction force countermass assembly, configuring an anti-gravity device to offset the weight of the stage to the assembly.
In a third preferred embodiment, the invention provides an exposure apparatus comprising: an illumination system that irradiates radiant energy; and an apparatus comprising: a stage; a reaction force countermass assembly; and an anti-gravity device between the stage and the reaction force-countermass assembly, the anti-gravity device configured to offset the weight of the stage to the reaction force-countermass assembly. In the inventive exposure apparatus, the apparatus disposes an object on a path of the radiant energy.
In a fourth preferred embodiment, the invention provides a device manufactured with the inventive exposure apparatus.
Further perfecting features of the inventive apparatuses and methods are as follows. The stage may be a reticle stage, such as a fine reticle stage or a coarse reticle stage. Anti-gravity devices may support the stage on a pair of reaction force-countermass assemblies located adjacent to the stage. The stage may be in contact with anti-gravity devices extending from a single reaction force-countermass assembly located on one side of the stage.